Lanthanide based primary luminescent thermometers for nanoparticle 3D localization using hyperspectral microscopy

Abstract

Recent advancements have made remote sensing through ratiometric luminescence thermometry, particularly based on trivalent lanthanide ions (Ln(III)), a promising technique with myriad applications. However, most existing Ln(III)-based luminescent thermometers requires a calibration process with a reference thermal probe (secondary thermometers), which needs recurrent calibrations, especially when used in diverse media. This calibration process can be impractical, leading to the postulation of a potentially inaccurate medium- independent calibration relation. Thus, the use of primary thermometers, based on well-established physical principles, becomes imperative to overcome these challenges. Despite their recognized importance in luminescence thermometry, primary luminescent thermometers are currently rare. In this study, we proposed, implemented, and validated primary thermometers requiring calibration at one known temperature (primary-T), which are also self-referencing, utilizing ratiometric data from the excitation spectra. Additionally, by combining with the emission spectra, we devised thermometers not requiring calibration (primary- S). While we demonstrated the feasibility of this approach using a Eu(III)-b- diketonate complex, the Eu(hfa)3bpyO2, as a proof-of-concept, the approach is universal, and other Ln(III)-based materials can be explored. Notably, the utilization of various thermometric parameters enabled unprecedented high accuracy of 0.2% in the physiological temperature range. We also explored the application of hyperspectral microscopy, an intriguing technique that combines spectroscopy with optical microscopy, to obtain simultaneous spectral and spatial information. Recent advances in optical reconstruction have enhanced the relevance of hyperspectral imaging in biomedical applications, such as monitoring bioimaging agents, identifying pathogens and cancerous cells, and assessing the cellular uptake of nanoparticles. In this context, we reported the synthesis of Yb(III)/Er(III)-codoped Gd2O3 nanoparticles, their structural and luminescence characterization, and their cell viability assessments in Human melanoma (MNT-1 and A375) cell lines. Using 2D hyperspectral imaging, we addressed the internalization of the particles by MNT-1 cells and their 3D localization in a fixed configuration across different planes and cell culture depths. The results demonstrated the distribution of particles in distinct planes deep within the cell volume, particularly in the cytoplasmic and perinuclear regions. Furthermore, using the emission of Yb(III)/Er(III)-codoped Gd2O3 nanoparticles the intracellular temperature was predicted with a value compatible with the room temperature.